Microscope with centered illumination

ABSTRACT

A microscope comprising a main objective having a variable focal length and comprising an illuminating unit including a light source and an illuminating optical system for generating an illuminating beam path directed onto the object plane and extending outside the main objective. A unit is provided for centering the illumination dependent on a variation of the focal length of the main objective. The illuminating optical system is mounted at least in part in a laterally shiftable manner for centering the illumination.

This application claims the priority of the German patent application DE10 2007 029 894.5 having a filing date of Jun. 28, 2007, the entirecontent of which is herewith incorporated by reference.

BACKGROUND OF THE INVENTION

The present invention relates to a microscope comprising a mainobjective having a variable focal length and comprising an illuminatingunit including a light source and an illuminating optical system forgenerating an illuminating beam path directed onto an object plane andextending outside the main objective, means being provided for centeringthe illumination dependent on a variation of the focal length of themain objective.

Microscopes of this type are known from DE 195 23 712 C2 and DE 195 37868 B4. In the first-mentioned DE 195 23 712 C2 a stereomicroscopecomprising a main objective with variable focal length, a downstreamzoom system and a binocular tube as well as an illuminating unitarranged adjacent to the main objective is disclosed. The main objectivecomprises a fixed and a movable lens for varying the focal length andthe intercept length of the main objective. The fixed, negative lens ofthe main objective is arranged towards the object plane, the movable,positive lens is arranged behind it (facing away from the object plane).A movement of the movable lens in the direction away from the objectplane results in a reduction of the focal length of the main objective.For an optimal illumination of the vertically shifting object plane, itis suggested in this document to adjust the position of an illuminationdeflector element dependent on a focal length variation of the mainobjective for centering the illumination. This is done in that the prismlens used as an illumination deflector element is pivoted such that theilluminating beam path tracks the shifted object plane. For thispurpose, the prism lens is pivotally mounted about an axis which isperpendicular to a plane that is spanned by the vertical optical axis ofthe main objective and the illuminating beam path which is incidentsubstantially horizontally inclined on the prism lens. As a resultthereof, for all positions of the movable lens of the main objectivefacing away from the object a focusing of the illuminating light on therespective focal point of the main objective can be guaranteed.

The coupling of the rotary movement of the illumination deflectorelement with the linear (vertical) movement of the lens of the mainobjective facing away from the object, as suggested in this document,requires very sensitive rotary movements of the illumination deflectorelement in relation to the movement of the lens and makes high demandson the mechanical coupling which is designed with a high constructionalexpense in this document. Any disturbances will be directly visible forthe user (particularly given high magnifications). Further, the size ofthe surface of the deflector element turns out to be disadvantageous, asit has to be sufficiently large in order to cover the entireilluminating pencil even when the illumination deflector element istilted. Mirrors or the mentioned prism lenses can be used asillumination deflector elements. When mirrors are used, an enlargementof the reflecting surface will result in the additional disadvantage ofan increased required thickness of the reflecting surface. Thus,altogether the required space and the height of the weight to be movedare increased.

In the mentioned DE 195 37 868 B4, an illuminating device for astereomicroscope comprising an objective with a variable image-formingintercept length is disclosed, an illumination intercept lengthvariation being possible via an optical system that is separate from theviewing optical system. Means for coupling the intercept lengthsmentioned are disclosed, which means effect that the illuminationintercept length and the image-forming intercept length correspond toone another. Further, means for coupling are provided which guaranteethat the angular position of a deflector element of the illuminatingdevice is varied such dependent on the respective image-formingintercept length and illumination intercept length that there is alwaysa centered illumination of the viewed field of view. Since, here too,for centering the illumination rotary movements of the illuminationdeflector element are performed, here, once again, the disadvantagesmentioned occur.

A basically different possibility of illumination centering results whenthe illumination is guided through the main objective of the microscope.This solution is implemented in the surgical microscope models M520 andM525 of the applicant. Here, the illumination deflector element directsthe illuminating beam path to and through the main objective havingvariable focal length so that the illumination is always centered on thefocus.

An optical binocular viewing system comprising one main objective commonfor both channels and a viewing zoom system as well as an illuminatingsystem having an illuminating zoom system is suggested in EP 0 321 586B2. The illuminating beam path is guided through the main objective viaa deflecting prism. The illuminating zoom system is adjusted dependenton the viewing zoom system in order to adapt the size of the illuminatedfield to the varying zoom magnification.

The microscopes mentioned up to now use vertical zoom systems, i.e. thelongitudinal axis of the zoom system lies parallel to the optical axisof the main objective. If, in addition, the illumination is fed into themain objective from above, there will be a high space requirement invertical direction resulting in microscopes having a relative highoverall height in the vertical direction. This is disadvantageous forergonomic reasons since the distance between the eyepiece and the mainobjective is increased.

From U.S. Pat. No. 6,473,229 B2, a stereomicroscope comprising ahorizontally arranged illuminating unit is known, the illuminating beampath of which being directed via a fixed deflecting mirror outside themain objective onto the object plane. The stereomicroscope suggestedtherein has a main beam path and an assistant beam path, for each of thetwo beam paths separate optical systems comprising a lens system, a zoomsystem and a binocular tube being provided. While one of the zoomsystems is designed such that it lies horizontally, the axis of theother zoom system is inclined to the vertical which is perpendicular tothe object plane. Here, with respect to illumination centering given avariable focal length of one of the lens systems no suggestions aremade.

For reducing the vertical constructional height, a stereomicroscopestructure has been suggested in EP 1 424 582 B1, in which a “lying” zoomsystem, i.e. a zoom system having its longitudinal axis arrangedhorizontally, is realized. For this purpose, there is arranged betweenthe main objective and the zoom system a deflector element whichdeflects the viewing beam path from a substantially vertical directioninto a substantially horizontal direction and feeds the same to the zoomsystem arranged in a first horizontal plane. By means of furtherdeflector elements the viewing beam path exiting the zoom system isdeflected into a second horizontal plane which extends substantiallyparallel to the first horizontal plane and in which optical add-oncomponents are arranged. With respect to details on the structure andthe mode of functioning of such a stereomicroscope with “lying” zoomsystem reference is explicitly made to the mentioned European patentspecification.

In this stereomicroscope, the illuminating unit is arrangedsubstantially adjacent to the main objective in horizontal direction undbelow the zoom system in vertical direction, the illuminating beam pathbeing guided outside the main objective. Instead of an illuminationcentering, it can be ensured by means of a sufficiently largeilluminated field that the visual field is always illuminated given afocal length variation of the main objective. Such a generously designedilluminated field requires a correspondingly largely designedilluminating aperture and thus illuminating unit which in turn has anegative effect on the ergonomics of the microscope. A furtherdisadvantage is here that the homogeneity of the illumination(distribution of the illuminated field) is not formed for all positionsof the multi-focus (variable focus lens). By using a variable focus lensdifferent object planes can be focused in a certain area.

The inventive microscope further comprises an illuminating unitincluding a light source and an illuminating optical system forgenerating an illuminating beam path directed onto an object plane andextending outside the main objective.

SUMMARY OF THE INVENTION

According to the invention, the illuminating optical system is mountedat least partially laterally shiftably for centering the illuminationdependent on a variation in focal length of the main objective. The term“laterally shiftably” means in this connection a shiftability not onlyin axial direction, i.e. not exclusively in the direction of theilluminating axis, but in a direction inclined thereto or perpendicularthereto, whereby an additional shifting component in axial directionshall not be excluded. It turned out that by means of such a lateralshifting of at least a part of the illuminating optical system, theilluminating focus can technically easily and reliably be tracked to thefocus of the main objective. Thus by a lateral shifting of theilluminating field said illuminating field tracks the field of view.Further, it turned out that it is sufficient to design only part of theilluminating optical system laterally shiftably. This is advantageoussince in this way not the entire illuminating unit has to be mountedshiftably but only a part of the actual illuminating optical system. Inaddition, a tracking of the illuminated field with respect to positionand size has the advantage that the diameter of the illuminated fieldcan be kept at a minimum and be adapted to the field of view so that inthe case of surgical microscopes the patient will be exposed to aminimum of radiation.

An illuminating unit used for the invention advantageously has, as seenfrom the light source, as an illuminating optical system a collector, adiaphragm as well as an illuminating lens assembly for focusing theilluminating beam path into the object plane. The opening of thediaphragm, often an iris diaphragm having a variable diameter, is imagedvia the lens assembly on the object plane given Köhler illumination.Other types of illumination as well as illumination units structuredotherwise can be used. An illumination deflector element can be arrangeddownstream or preferably upstream of the illumination lens assembly. Asa result thereof, it is in particular possible to use an illuminatingunit (for example light source, collector and diaphragm) arranged atleast partially horizontally and to deflect the generated illuminatingbeam path by means of the illumination deflector element in a verticaldirection in the direction of the object plane.

It turned out that in particular in case of this kind of structure of anilluminating unit, it is sufficiently according to the invention tomount only the mentioned lens assembly or a part thereof laterallyshiftably. The illumination lens assembly itself can in principlerepresent a single lens or a combination of lenses. Instead of thelateral shiftability of the entire lens assembly it can be sufficient inthe last case, if only one or specific lenses of the combination oflenses are laterally shifted to achieve the desired centering of theillumination.

As mentioned, the illuminating unit is often at least partially arrangedsuch that the generated illuminating beam path is incident on theillumination deflector element in a direction that is substantiallyperpendicular (or inclined) to the optical axis of the main objective,which, without restricting the generality, is substantially verticallydirected (“horizontal illuminating unit”). The illumination deflectorelement deflects this illuminating beam path then in the direction ofthe object plane on the focus of the main objective. This section of thedeflected illuminating beam path encloses a specific angle with thevertical (normal to the object plane). Given a variation of the focallength of the main objective which results in a shifting of the imagedobject plane in vertical direction given this arrangement, this anglelikewise has to be varied so that the illumination remains centered.Surprisingly, it turned out that this variation of said angle can simplybe done by a lateral shifting of the illumination lens group (inparticular of the illumination lens group downstream of the deflectorelement). In particular, a linear shifting of the illumination lensassembly is sufficient and this shifting can take place preferablyparallel to the object plane in the case of a lens assembly arrangeddownstream of the deflector element.

With respect to the orientation of the lens assembly two advantageousembodiments shall be mentioned: Firstly the symmetrical axis of the lensassembly can be aligned parallel to the axis of the illuminating beampath. The lateral shifting can for example again take place parallel tothe object plane in the case of the above-mentioned microscopeillumination arrangement. As a consequence the lens assembly is thentiltably arranged with respect to the lateral direction of movement. Inthe case of a circular lens and diaphragm geometry, the illuminatingfield generated on a horizontal object plane in this case has anelliptic geometry, as the axis of the illuminating beam path is notperpendicular to the object plane. As a consequence, the orientation ofthe lens assembly can be utilized systematically to influence thegeometry of the illuminating field. For example, the symmetrical axis ofthe lens assembly can be aligned perpendicular to the object plane inanother case and remain aligned in this way during the lateral shifting.In principle it would also be conceivable to change the orientation ofthe lens assembly during a lateral shifting, for example in order tomake corrections of the illuminating field geometry.

In principle, also other lateral shiftings are conceivable, for examplesuch shiftings, which are perpendicular on the illuminating axis comingfrom the illumination deflector element or shiftings along a curvedpath, thus, for example along a circular path of a circle with thecenter in the illumination deflector element. However, the mentionedlateral shifting parallel to the object plane proved to be realizable ina particular easy and technically reliable manner in case of thestructure of the illuminating unit described here.

It is expedient if a control unit for coupling a variation of the focallength of the main objective with an amount of lateral shift of the atleast one part of the illuminating optical system is provided. Here, itis useful, with respect to the specific microscope structure comprisingthe specific illuminating unit, to assign at least for a number ofworking distances (or, respectively, focal lengths of the mainobjective) the correspondingly necessary lateral shift amounts and toderive a corresponding relationship therefrom (numerical or in the formof a formula), which is afterwards entered into a corresponding control.The mentioned relationship can also be established with the aid ofsuitable software by ray tracing given different working distances and abest-fit method. A closed loop control of the illumination centering canalso be considered.

It is noted that the features of the invention which have already beenmentioned and which are still to be mentioned cannot be used only in thecombination given herein but, as far as technically useful, also aloneor in other combinations, without leaving the scope of the presentinvention.

In the following, an embodiment illustrated schematically in the drawingshall explain the invention and its advantages in more detail.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically shows the structure of a microscope with which theinvention can preferably be used.

FIG. 2 shows the influence of a varied operating distance on theillumination centering.

FIG. 3 schematically shows a cutout of the microscope according to FIG.1, which only shows the essential components of the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically shows the basic structure of a microscope 10, heredesigned as a surgical stereomicroscope, for a better illustration onlythe viewing axis R_(o) being illustrated. Such surgical microscopesoften have an additional pair of viewing beam paths for assistant'sviewing in addition to a pair of main viewing beam paths. Microscopes ofthis type are known per se and therefore are not to be explained in moredetail here. In this connection, reference is made to thestereomicroscope described in the already mentioned EP 1 424 582 B1 inwhich, as in the present case, a “lying” zoom system 30 is realized.

The surgical microscope 10 comprises a main objective 20 which isdesigned as a multi-focus (or variable focus lens), i.e. represents alens having a variable focal length. The main objective 20 defines anoptical axis 23 which is perpendicular to an object plane 100. Byvarying the focal length of the main objective 20, focusing on therespective object plane 100 can be effected. The viewing beam paths runparallel to the shown optical axis 23 and lie, for example, either inthe drawing plane or in a plane perpendicular to the drawing plane andincluding the optical axis 23. For deflecting the viewing beam paths afirst deflector element 50 is arranged in the beam path and deflects theviewing beam paths from a substantially vertical direction into asubstantially horizontal direction into the “lying” zoom system 30. Thezoom system 30 is arranged with its longitudinal axis in a firsthorizontal plane I. Instead of a zoom system 30 which serves for thecontinuous magnification of the object image a discretely operatingmagnification changer can likewise be provided. By means of furtherdeflector elements 51 and 52, the viewing beam path is directed into asecond horizontal plane II. Here, the tube 60 is arranged, which directsthe illuminating beam path into at least one eyepiece 70 through whichan observer 110 can view the microscope image. The principle structureof the described microscope components such as main objective, zoomsystem, tube and eyepiece or binocular tube is common knowledge for theperson skilled in the art. In the beam path illustrated in FIG. 1,optical add-on components such as filters, image inverters, componentsfor extending the optical path length, beam splitters for assistant'sviewing and reflecting-in and reflecting-out devices (for example datareflecting-in devices) etc. can be arranged. Finally, between the zoomsystem 30 and the tube 60 an output (optical/mechanical) fordocumentation (camera, video, etc.) can be present.

An illuminating unit 40 which can be arranged ergonomically favorablewith its longitudinal axis substantially horizontally below the zoomsystem 30 serves for the illumination of the object. What is illustratedhere is a fiber illumination via a light guide 80. However, a directhalogen, xenon or LED illumination can likewise be used. Theilluminating beam path generated by the illuminating unit 40 andillustrated by means of its illuminating axis R_(i) is directed by meansof an illumination deflector mirror 43 in the direction of the objectplane 100. As can be taken from FIG. 1, the illuminating beam path isguided outside the main objective 20 of the microscope 10. Therefore,given a focal length variation of the main objective 20 resulting in ashifting of the object plane 100 in vertical direction, the illuminatingbeam path has to be tracked for an optimal illumination. The inventivetype of this tracking of the illumination shall be explained in moredetail on the basis of FIG. 3.

As can be taken from FIG. 1, the axis R_(i) of the illuminating beampath encloses the angle θ with the axis R_(o) of the viewing beam path.

FIG. 2 illustrates the required change of the mentioned angle θ given afocal length variation of the main objective 20 or given a variation inthe working distance between this main objective 20 and the object plane100. With decreasing focal length of the main objective 20 and thusdecreasing working distance, the angle θ is increased. FIG. 2 shows twoextreme positions, for example maximum and minimum working distance, theaxis R_(i2) of the illuminating beam path being directed onto the focusof the main objective 20 given a greater working distance. Here, theangle θ₂ results. Given a smaller working distance, the angle θ has tobe increased, until, for example, the angle θ₁ with the associatedilluminating axis R_(i1) is reached. From the maximum and the minimumworking distance of the main objective 20, thus a range for the angle θcan be given which is to be tracked given a change in the workingdistance in order to achieve a centered illumination.

FIG. 3 now shows the measures necessary therefor according to theinvention in a specific embodiment. In FIG. 3, the structure of anilluminating unit 40 is illustrated, as it shall preferably be used forthe present invention. The collector (here with the light source) isdesignated with 41. The collector collects the light from the lightsource and images the same via the diaphragm 42 and the illuminatinglens assembly 44 into the object plane 100. The diaphragm 42 concernedis preferably an iris diaphragm with variable diameter. A plane mirroror also a spherical mirror can be used as an illumination deflectorelement 43. The illumination lens assembly 44 is preferably (as viewedfrom the light source) arranged downstream of the illumination deflectorelement 43. This is a difference to the illuminating unit 40, as it hasbeen described in FIG. 1. The illuminating lens assembly 44 canrepresent a single lens or (as usual) a combination of lenses. In thisembodiment the symmetrical axis of the lens assembly 44 is orientatedperpendicular to the object plane 100. To simplify matters, the entirelens assembly 44 is illustrated laterally shiftably in FIG. 3. However,it shall be emphasized that it can be sufficient in case of amany-membered structure to design only individual parts of this lensassembly laterally shiftably. In particular, also individual parts ofthis lens assembly could be arranged upstream of the illuminationdeflector element 43, others could be arranged downstream of theillumination deflector element 43.

By means of lateral shifting of the lens assembly 44 the illuminatingbeam path and thus the axis R_(i) thereof can be tracked to a changingfocus of the main objective 20. For example, in case of a changingworking distance according to FIG. 3 the transition of the angle θ fromθ₂ to θ₁ is carried out by a lateral shifting, as illustrated in FIG. 3,of the lens assembly 44 towards the left, i.e. in the direction of themain objective 20. The lateral shifting in this embodiment takes placealong a line of intersection of two planes, one of said planes extendingparallel to the object plane 100 and the other one of said planes beingspanned by the axes R_(o) and R_(i).

Deviating from the arrangement illustrated in FIG. 3 also slightmodifications can be applied. For example, the lens assembly 44 can in aspecific lateral position coincide with the optical axis thereof withthe axis R_(i) of the illuminating beam path. Further, instead of ashifting parallel to the object plane 100 also a shifting perpendicularto the axis R_(i) of the illuminating beam path can be carried out. Asalready mentioned, circular arc shifts, for example along a circular arcwith the center in the point of incidence of the axis R_(i) on thedeflector element 43, are also conceivable. However, here it has to betaken into account that a coupling of the focal length variation of themain objective with a linear movement of the lens assembly 44 can berealized in a technically easier way than the coupling with a rotarymovement. In this connection, it is moreover pointed out once again thatthe deflector element 43 does not have to be tiltably mounted about anaxis, as the lateral shifting of the lens assembly is alone suitable tomake an illumination centering within the possible operating distancesof the main objective 20 possible.

It is advantageous when a control unit 90 is provided for the couplingof a variation of the focal length of the main objective with an amountof the lateral shifting of the lens assembly 44 of the illuminating unit40. The control unit 90 is schematically illustrated in FIG. 3, a signalbeing supplied to the control unit via an input thereof, which signalindicates a variation of the focal length of the main objective 20 andthe respective required amount of shifting of the lens assembly 44 beingoutput via an output of the control unit 90. The relation between theamount of shift and the variation in focal length can practically beestablished in a simple way with the aid of known software by theso-called “ray tracing” and a best-fit method. The lateral shifting ofthe illuminating axis R_(i) on the object plane 100 hereby depends onthe image scale of the lens assembly 44 and the lateral shifting of thislens assembly 44.

The possibilities of varying the focal length of a main objective 20have already been mentioned in the introductory part of thespecification. Common is the combination of a fixed and a movable lensfor varying the focal length and the intercept length of the mainobjective. The movement of the movable lens can be measured directly andcan be assigned to the varying intercept length of the main objective orits working distance. Altogether, the illumination centering accordingto the invention can thus be put into practice with known controlmethods.

LIST OF REFERENCE NUMERALS

-   10 microscope-   20 main objective-   23 optical axis-   30 zoom system-   40 illuminating unit-   41 collector-   42 diaphragm, iris diaphragm-   43 illumination deflector element-   44 lens assembly-   50 deflector element-   51 deflector element-   52 deflector element-   60 tube-   70 eyepiece-   80 light guide-   90 control unit-   100, 100′ object plane-   110 observer-   I first horizontal plane-   II second horizontal plane-   R_(o) viewing axis-   R_(i) illuminating axis-   θ angle R_(i) to R_(o)

1. A microscope comprising: a main objective having a variable focallength; an illuminating unit comprising a light source and anilluminating optical system for generating an illuminating beam pathdirected onto an object plane and extending outside the main objective;and means for centering the illumination dependent on various focallengths of the main objective; wherein the illuminating optical systemis at least in part mounted in a laterally shiftable manner forcentering the illumination; the illuminating unit has as an illuminatingoptical system a collector, a diaphragm, an illumination deflectorelement as well as a lens assembly for focusing the illuminating beampath onto the object plane; and the symmetrical axis of the lensassembly is aligned perpendicular to the object plane.
 2. The microscopeaccording to claim 1, wherein the illuminating optical system has a lensassembly that is at least in part mounted in a laterally shiftablemanner.
 3. The microscope according to claim 2, wherein the illuminationdeflector element has a fixed position.
 4. The microscope according toclaim 1, wherein the illuminating optical system has a lens assemblythat is at least in part mounted in a laterally shiftable manner.
 5. Themicroscope according to claim 1, wherein the illumination deflectorelement has a fixed position.
 6. The microscope according to claim 1,wherein the lens assembly is at least in part shiftably mounted parallelto the object plane.
 7. The microscope according to claim 1, wherein acontrol unit for coupling a variation of the focal length of the mainobjective with an amount of lateral shift of the at least one part ofthe illuminating optical system is provided.
 8. The microscope accordingto claim 1, wherein the microscope comprises a zoom system arrangeddownstream of the main objective as viewed from the object plane.
 9. Themicroscope according to claim 8, wherein a deflector element is arrangedbetween the zoom system and the main objective, said deflector elementdirecting the viewing beam path coming from the main objective into afirst horizontal plane in which the longitudinal axis of the zoom systemlies.
 10. The microscope according to claim 9, wherein that themicroscope comprises a tube and at least one eyepiece which are arrangeddownstream of the zoom system, and at least the tube is arranged withits longitudinal axis in a second horizontal plane which runssubstantially parallel to the first horizontal plane.
 11. The microscopeaccording to claim 1, wherein the microscope comprises a tube and atleast one eyepiece that are arranged downstream of the zoom system. 12.The microscope according to claim 1, wherein the microscope is designedas a stereomicroscope.
 13. The microscope according to claim 12, whereinthe microscope is designed as a surgical microscope.
 14. A microscopecomprising: a main objective having a variable focal length; anilluminating unit comprising a light source and an illuminating opticalsystem for generating an illuminating beam path directed onto an objectplane and extending outside the main objective; and means for centeringthe illumination dependent on various focal lengths of the mainobjective; wherein the illuminating optical system is at least in partmounted in a laterally shiftable manner for centering the illumination;the illuminating unit has as an illuminating optical system a collector,a diaphragm, an illumination deflector element as well as a lensassembly for focusing the illuminating beam path onto the object plane;and the symmetrical axis of the lens assembly is aligned parallel to theaxis (R_(i)) of the illuminating beam path.
 15. The microscope accordingto claim 14, wherein the illuminating optical system has a lens assemblythat is at least in part mounted in a laterally shiftable manner. 16.The microscope according to claim 15, wherein the illumination deflectorelement has a fixed position.
 17. The microscope according to claim 14,wherein the illuminating optical system has a lens assembly that is atleast in part mounted in a laterally shiftable manner.
 18. Themicroscope according to claim 14, wherein the illumination deflectorelement has a fixed position.
 19. The microscope according to claim 14,wherein the lens assembly is at least in part shiftably mounted parallelto the object plane.
 20. The microscope according to claim 14, wherein acontrol unit for coupling a variation of the focal length of the mainobjective with an amount of lateral shift of the at least one part ofthe illuminating optical system is provided.
 21. The microscopeaccording to claim 14, wherein the microscope comprises a zoom systemarranged downstream of the main objective as viewed from the objectplane.
 22. The microscope according to claim 21, wherein a deflectorelement is arranged between the zoom system and the main objective, saiddeflector element directing the viewing beam path coming from the mainobjective into a first horizontal plane in which the longitudinal axisof the zoom system lies.
 23. The microscope according to claim 14,wherein the microscope comprises a tube and at least one eyepiece thatare arranged downstream of the zoom system.
 24. The microscope accordingto claim 22, wherein the microscope comprises a tube and at least oneeyepiece which are arranged downstream of the zoom system, and at leastthe tube is arranged with its longitudinal axis in a second horizontalplane which runs substantially parallel to the first horizontal plane.25. The microscope according to claim 14, wherein the microscope isdesigned as a stereomicroscope.
 26. The microscope according to claim25, wherein the microscope is designed as a surgical microscope.